1. Field of the Invention
The present invention relates generally to couplers for model railroad rolling stock, and more particularly, to such couplers that can be remotely coupled and uncoupled, provided in small scales, and made to closely resemble full scale railroad couplers in operation and appearance.
2. Description of Related Art
Model railroad equipment comes in many scales, some of the most popular of which result in extremely small replicas of full scale railroad equipment. Avid model railroaders insist on realism, in both operation and appearance, regardless of how small their scale model equipment is. For the most part, it is a fairly simple matter to reduce the scale of railroad rolling stock and accessories such as scenery items and buildings used in layouts that simulate an actual landscape. However, couplers for the rolling stock present a special challenge when reducing them to sizes compatible with scales commonly used in model railroading.
Model railroads can come in extremely small scales. For example, N scale is 1:160, which is about one-half the size of the HO scale (1:87) more familiar outside model railroading circles, and Z scale is even smaller (1:220). Smaller scales enable simulation in the same amount of space of a more elaborate and diverse landscape, with the result that N and Z scales have become very popular with model railroading enthusiasts. Providing a properly functional coupler that is as realistic as possible becomes a serious challenge as the scale gets smaller. Model railroad layouts must be capable not only of realistically duplicating the appearance of a full-scale landscape, but all of the railroad components themselves, including couplers, should also be capable of simulating the operation of a full-scale railroad to the greatest extent possible. This requires that the model railroader operating a layout be able to assemble various items of rolling stock into trains, disassemble trains, store rolling stock in a simulated train yard that is part of the layout, retrieve stored rolling stock to incorporate into a train when desired, and otherwise provide a realistic railroading experience. Obviously, this involves performing coupling and uncoupling operations and moving coupled and uncoupled rolling stock to desired locations in the layout. Preferably, the couplers permit coupling and uncoupling rolling stock to be performed at a distance remote from a central control location where the operator of the model railroad layout might be running multiple trains at any given time.
Model railroad couplers are generally available commercially in essentially three different styles. One popular style is the Magne-Matic® coupler marketed by Micro-Trains Line Co. of Talent, Oreg., the construction of which coupler is exemplified by U.S. Pat. No. 3,469,713. This type of coupler is known as a split-shank coupler, because it has two separate shanks, one carrying a coupler knuckle and the other carrying a coupler lip. The shanks are pivotably mounted to permit the rolling stock to follow curved track portions without derailing. The pivotal mounting also allows the two shanks to move relative to each other to separate the coupling parts (the knuckle and lip) and effect coupling/uncoupling operations like those discussed above and in more detail further below in connection with the present invention.
The Magne-Matic® coupler can carry out remote coupling/uncoupling operations effectively and reliably. However, the spring system used to bias the shanks centrally of a coupler housing during straight-line travel of the rolling stock, and also into a coupled state in which the coupler parts are in their closed positions, has a significant amount of “play” in the direction of train movement. This can be appreciated from, say, FIG. 6 of the '713 patent, which shows a smaller diameter mounting post (40) within larger central openings in the shanks (50,54). In a commercial model of this coupler the resulting space allows from about 0.010″ to 0.020″ of relative motion between the shanks and the post. One issue arises because various train operations exert a force on the coupled railroad cars tending to separate them in the direction of train travel. While the couplers prevent the railroad cars from actually separating, the space between the mounting post and the shanks' central openings can delay the motion of subsequent cars in a train when a locomotive begins to pull on the first car. For example, if a train is 50 cars long, the first car might have to travel as much as 1-2″ (0.010″ to 0.020″ times 100—there being two couplers per car) before the last car begins to move. In addition, the train can undergo a cyclical telescoping motion because the biasing compression springs contract and expand while the train is moving, which can cause periodic lengthening and contracting of the train known to modelers as the “Slinky” effect (after the familiar Slinky® spring toy). Another issue with Magne-Matic® couplers is that the shanks and mounting box must be long enough to accommodate the biasing spring, which can cause the coupler to protrude an excessive distance from certain types of model rolling stock and detract from a realistic appearance.
A second popular coupler style is also a split-shank coupler, sold by Accurail Inc. of Elburn, Ill., under the Accumate® brand, one type of which is shown in FIG. 1 (from a document available at http://www.accurail.com/accurail/parts.htm). This coupler has an upper shank US that carries a coupler lip L and a lower shank LS that carries a coupler knuckle K. Each shank has an opening O that fits over a post P when the coupler is assembled into the mounting box B and a biasing spring BS that bears against an inside surface of the mounting box B. Each shank is also independently pivotable about an axis defined by the post P, so that the springs BS center the shanks in the box for straight-line travel of coupled rolling stock, and at the same time allow the shanks to pivot independently to perform an uncoupling operation when a magnetically operated actuation pin AP causes rotation of the lower shank LS to which it is attached.
This coupler style is acceptable to a large number of railroad modelers, but it too has drawbacks. For one thing, the biasing springs BS are molded as integral parts of the plastic shanks US and LS. Being plastic, the springs generally lose their resilience over time, which can affect the operation of the coupler. It is also difficult to mold a plastic leaf spring like the biasing springs BS so that it has a spring constant within acceptable tolerances for proper coupler operation. For example, if the springs are too stiff they can impede the ability of the coupler to pivot as the small, light-weight model rolling stock travels curved track sections, thus making the train prone to derailing. In addition, a plastic spring tends to have a “memory” that will preserve at least some of a deformation imposed on the spring for a long period, such as when a train is parked on a section of curved track for an extended time. This can impair subsequent operation of the train (since the permanently deformed biasing springs will impose a lateral force on the rolling stock when it is on a section of straight track), and can affect coupling/uncoupling operations as well.
Another drawback of this coupler style is that having the lip L on the upper shank somewhat affects the ability of the coupler to be made to look as realistic as it might otherwise be if the knuckle-bearing shank were on top, as shown in Accurail U.S. Pat. No. 5,620,106. However, the coupler in the '106 patent is not remotely actuatable, largely because the lower shank (13) is too thin to hold an actuating pin (AP in FIG. 1) in place against the torque applied to it during an automatic uncoupling operation. As seen in FIG. 1, with the knuckle-bearing shank on the bottom, the actuating pin AP can be secured in a relatively thick knuckle section using a keying arrangement, such as the flat portions at the top of the actuating pin AP, to prevent relative rotation between the pin and the knuckle.
A third popular model railroad coupler style on the market today is sold by McHenry Couplers of Long Beach, Calif. This coupler has a single shank with a proximal end pivotably mounted to a piece of rolling stock and a rotatable, spring-biased knuckle forming a coupler at a distal end of the shank. Centering springs at the proximal end of the shank urge the coupler into a position aligned with the rolling stock's longitudinal centerline, while also permitting the shank to deflect from side-to-side as discussed above to enable coupled rolling stock to negotiate curved track sections. Reference may be made to U.S. Pat. No. 5,662,229 and U.S. Pat. No. RE38,990 to see certain features of this type of coupler, although neither patent exactly depicts the structure of commercially available McHenry™ couplers.
Although McHenry™ couplers have proved popular among modelers, they also present certain problems. The commercial version of the coupler has plastic centering springs somewhat like those shown in the '990 patent, which are of course subject to the drawbacks of plastic springs discussed above. In addition, the coupler knuckle is biased into the closed position by a large external spring that detracts from the realistic appearance of the coupler, as shown in FIG. 2, which is a photograph of a commercially available McHenry™ coupler (from “Knuckle Couplers” at http://members.cox.net/mrobbins1/Couplers.pdf). Compare FIG. 2 with FIG. 3, which is a photograph of an actual railroad coupler. It will be readily apparent that the model version (FIG. 2) is not a particularly accurate replica of the actual coupler (FIG. 3).
In addition to the drawbacks of the three magnetically actuated coupler styles generally available commercially to modelers today, the only one of the three available for Z scale rolling stock is the Magne-Matic® coupler, which has the issues discussed above. There are patents that describe couplers that seek to ameliorate some of the drawbacks noted above with other style couplers. For example, U.S. Pat. No. 5,662,229 uses metal centering springs for a McHenry style coupler, in an attempt to avoid problems caused by plastic springs, but according to the patent the described design appears to be particularly adapted for HO scale. With smaller rolling stock, especially Z scale, it is believed that manufacturers and modelers would find it difficult as a practical matter to reliably attach thin wire centering springs to a mounting plate as shown in the '229 patent. U.S. Pat. No. RE38,990 replaces with a cantilever spring the unsightly external coil spring of commercially available McHenry style couplers, but so far as is known the operability of such a design has not been established, and it still does not provide a completely realistic looking coupler. Finally, U.S. Pat. No. 6,994,224 replaces the McHenry external coil spring with a spring located out of sight inside the coupler knuckle. However, the extremely small dimensions necessary in Z scale (or even N scale) probably make this design impracticable for these smaller scales.
Accordingly, there is a need for a model railroad coupler, particularly for N scale and Z scale rolling stock, that is remotely actuatable, reliable, avoids the necessity of using plastic springs, and can be made as realistic as possible in both operation and appearance.